1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) and, more particularly, to an LCD including a fluorescent color filter and an intra-cell polarizer formed on the fluorescent color filter, and a fabrication method thereof.
2. Discussion of the Related Art
Recently, as diverse portable electronic devices such as mobile phones, PDAs or notebook computers are being developed, a flat panel display (FPD) which is light, thin, short and small and can be applicable to the portable electronic devices is increasingly required. As the FPD, the LCD, a PDP (Plasma display panel), an FED (Field Emission Display), a VFD (Vacuum Fluorescent Display) and an OLED (Organic Light Emitting Device), etc. are actively studied, and among them, the LCD is receiving much attention because of its mass-production techniques, easiness of its driving unit and implementation of high picture quality.
FIG. 1 is an exploded perspective view of a general LCD according to the related art. As shown, the LCD includes a liquid crystal panel 10 and a backlight unit 20.
The liquid crystal panel 10 includes first and second substrates that face each other and a liquid crystal layer (not shown) formed between the two substrates.
Because the liquid crystal layer has an optical anisotropy, when an electrical signal is applied thereto, an alignment of liquid crystal molecules is controlled to display an image. Of the two substrates, thin film transistors TFTs are positioned on the first substrate and an image is displayed according to an ON/OFF of the TFTs.
The liquid crystal panel 10 is connected with a gate and source PCB (Printed Circuit Board, not shown) that applies an image signal and a scan signal to the liquid crystal panel 10.
Since the liquid crystal panel 10 cannot illuminate by itself, a light providing unit is required. So the liquid crystal panel 10 includes a backlight unit having a light source that provides light. The backlight unit 20 is divided into a direct type backlight unit and an edge type backlight unit depending on how a light source is disposed. The direct type backlight unit is applied for a relatively large LCD while the edge type backlight unit is applied for a relatively small LCD. The backlight unit used for the illustrated LCD in FIG. 1 is the edge type backlight unit.
In the LCD having the edge type backlight unit, a light source 21 that provides light is disposed on at least one lateral surface of the liquid crystal panel 10, and a light guide plate 24 that has at least one surface facing the light source 21 and guides light emitted from the light source 21 to the liquid crystal panel 10. Namely, the light source 21 is positioned in a lengthwise direction at the side of the light guide plate 24. Light emitted from the light source 21 is made incident to one side of the light guide plate 24, refracted and reflected in the light guide plate 24, and then outputted in a direction of the liquid crystal panel 10.
An optical films 23 such as a diffusion plate and/or a prism plate is stacked at an upper portion of the light guide plate 24 in order to diffuse the light made incident from the light source 21 to make it irradiated onto the liquid crystal panel 10. The optical films 23 serve to effectively diffuse and collect the light outputted from the light guide plate 24.
As the light source 21 of the backlight unit, a cold cathode fluorescent lamp (CCFL) is commonly used.
When current having high voltage flows to electrodes of both ends of the CCFL via an electric wire, electrons are emitted from the both ends of the electrode 56. The electrons make mercury(Hg) contained in the discharge gas be excited to a state of a high energy level.
Mercury in the excited state falls to a ground state, emitting ultraviolet rays. The ultraviolet rays change an energy level of fluorescent materials coated on an inner wall of a transparent tube. The fluorescent materials absorb these ultraviolet rays and finally emit white light of a visible ray region.
In order to implement an image by using liquid crystal, the light source 21 is required. However, a transmission light emitting from the light source 21 includes vibration vectors that are not required for the liquid crystal panel. So in order to control the vibration vectors of the transmission light, polarizers 15a and 15b are attached on both surfaces of the liquid crystal panel 10 such that the transmission axis of each polarizer cross at 90° with respect to each other.
The polarizers 15a and 15b polarize a transmission light which has passed through the liquid crystal layer into light with a particular vibration vector. Thus, while passing through the liquid crystal panel 10, intensity of the transmission light is controlled according to a rotation degree of a polarization axis, enabling expression of black to white. Such transmission light can appear images of various colors after passing through color filters.
FIG. 2 shows schematically a section of a general liquid crystal panel.
As shown, an LCD panel 10 includes a first substrate 5, a second substrate 3 and a liquid a crystal layer 7 formed between the first and second substrates 5 and 3. The first substrate 5 includes a TFT 9 formed thereon. Although not shown, a plurality of pixels are formed on the first substrate and each pixel includes the switching devices such as the TFTs 9.
The second substrate 3 includes color filter 2 for implementing colors, and is formed to face the first substrate 5 with the liquid crystal layer 7 interposed therebetween. A black matrix 8 for blocking light is formed on the second substrate 3.
In addition, a pixel electrode 6 and a common electrode 4 are formed on the first and second substrates 5 and 3, respectively, and an alignment layer (not shown) for aligning liquid crystal molecules of the liquid crystal layer 7 is coated on the substrates to determine orientation of the liquid crystal molecules.
In the liquid crystal panel 10, liquid crystal molecules are driven by the switching device formed as the TFT 9 on the first substrate 5 to control the intensity of light transmitting through the liquid crystal layer to thus display information.
In fabricating the first and second substrates, the first substrate 5 includes a process of forming the TFT 9 on the first substrate 5, and the second substrate 3 includes a process of forming the color filter 2.
The first substrate process includes forming a plurality of gate lines and a plurality of data lines that define pixel regions, and forming the TFTs 9 connected with the gate lines and the data lines. The pixel electrodes 6 are also formed to be connected with the TFTs 9 to drive the liquid crystal layer 7.
The second substrate process includes forming the black matrix 8 on the second substrate 3, forming the color filters 2 thereon, and forming the common electrode 4.
The color filter includes the three primary colors of red, green and blue. When light emitted from the backlight unit passes the color filter, only one of the three primary colors passes while the other remaining colors are absorbed. Thus, when light passes through the color filter, the color which has passed through the color filter excluding the absorbed colors are recognized by humans' eyes.
However, the problem of the color filter is that it allows only one of the R, G and B colors to pass therethrough, and absorbs the most portions of the white light, causing a loss of about two-thirds of the light emitted from the backlight unit by the color filter.
In addition, because light absorption also occurs from elements for forming the liquid crystal panel, namely, from the TFT or the liquid crystal layer itself, resulting in degradation of the overall light transmittance of the LCD and luminance.
Thus, in order to solve the problem, a brighter light source should be used, or a plurality of light sources should be used and a driving voltage of the light sources should be increased.